1. Field of Invention
The present invention relates to a burner, and more specifically to a centrally fuel rich (CFR) swirl coal combustion burner which can reduce the output of the emissions amount of NOx.
2. Description of Related Arts
Nitrogen Oxide (NOx) is one of the main contaminants for air pollution. It not only forms the acid rain to damage the ecological environment, but also forms the actinic fog to harm the health of human being. The coal combustion is one of the main sources of the generation of nitrogen oxide compound. At the present, there are two methods to control the formation of NOx. The first method is low NOx combustion technology which can reduce the formation of NOx. The second method is the flue gas denitrification which applies removing reactant of denitrification to the flue gas to remove NOx. China Patent, CN1207511C, publication date of Jun. 22, 2005, entitled “Centrally Fuel Rich (CFR) Swirl Coal Combustion burner”, teaches the control of the formation of NOx, as the first method, to control the formation of NOx. Accordingly, the burner comprises a pulverized separator having a cone shape to collect the pulverized coal at the central portion of a primary air-coal mixture duct, wherein the injection of the pulverized coal is aligned with a center of the central recirculation zone of the burner. Throughout the combustion of the pulverized coal, the concentration of the pulverized coal is increased within the central recirculation zone while the residence time of pulverized coal is prolonged to reduce the formation of NOx. However, there is no conical outlet installed at the outlets of the primary air-coal mixture, inner and outer secondary air ducts, the pulverized coal at the primary air-coal mixture and inner and outer secondary air ducts is parallelly spurted into the furnace so that the central recirculation zone formed by the swirl of the secondary air is relatively small. Thus, the residence time of pulverized coal in the central recirculation is not long enough to inhibit the formation of nitrogen oxide compound at most. Also, without the conical outlet, the air through the primary air-coal mixture and secondary air ducts is mixed immediately into the furnace, so that the ability of NOx reduction is substantially decreased. Therefore, it cannot effectively inhibit the formation of NOx. Furthermore, the major drawbacks of the second method of controlling the nitrogen oxide compound, through the flue gas denitrification by applying removing reactant of denitrification to flue gas to remove nitrogen oxide compound, are high investment cost and operating cost.